1. Field of the Invention
The present invention relates to a method of fabricating a thin film transistor formed by doping an active layer with impurities by using a gate as a mask and by forming a source and a drain by activating the impurities.
2. Discussion of the Related Art
FIGS. 1A-1C show cross-sectional views of a TFT structure which illustrates a method for fabricating a thin film transistor (hereinafter abbreviated TFT) according to a related art.
In FIG. 1A, an insulating or buffer layer 13 is formed by depositing an insulating substance, such as silicon dioxide, on a transparent substrate 11, such as a glass substrate or the like, with Chemical Vapor Deposition (hereinafter abbreviated CVD). An active layer 15 is formed by depositing polycrystalline silicon on the buffer layer 13 with CVD. Next, the active layer 15 is patterned by photolithography to be etched on a predetermined portion of the buffer layer 13.
According to FIG. 1B, another layer of silicon dioxide is now grown or deposited across the surface of the silicon wafer. Using similar lithographic techniques to those described above, holes are etched through the silicon dioxide in areas in which it is desired to make the connections and metallization layer of aluminum interconnections are deposited. In other words, after the silicon dioxide layer covers the active layer 15, a conductive material such as Aluminum, metal, or the like is deposited on the silicon dioxide layer by the CVD process.
A gate insulating layer 17 and a gate 19 are formed by patterning the conductive material and the silicon dioxide layer by photolithography so that they remain over a selected portion of the active layer 15.
Subsequently, ion-implanted region 21, constituting source and drain regions, is formed by heavily doping an exposed surface of the active layer 15 with impurities such as Phosphorous (P), Arsenic (AS), or the like, by using the gate 19 as a mask.
Referring to FIG. 1C, the impurities implanted in the ion-implanted region 21 are activated by application of a laser beam onto the region 21. Consequently, an impurity region 23 constituting a source and a drain is formed as the impurity ions in the region 21 are activated by the laser beam.
However, as the above-described method of fabricating a TFT according to the related art reveals, this process involves complicated steps, such as irradiation of the impurity region with a laser beam to form a source and a drain region and activation of the implanted impurity ions.
The use of laser beams are costly, not very feasible, and can significantly increase the risk of structural damage to the semiconductor layers because of its heat treatment intensity.